The cost of forest thinning operations in the United States West: a systematic literature review and model development

Increases in tree regeneration have led to dense forests in the western United States, which has increased hazardous fuels and created favorable environments for landscape-scale wildfires. Mechanical forest thinning treatments have been implemented across the U.S. West to improve forest health and reduce hazardous fuels. However, the main challenge for implementing forest thinning treatments is their economic feasibility because forest thinning treatments require high-cost while they typically focus on harvesting low-value, small-diameter trees. This study was conducted to synthesize the stump-to-truck cost of forest thinning treatments based on research articles published over the last 40 years (1980-2020). I systematically selected and reviewed 21 thinning studies to analyze key variables affecting machine productivity and harvesting costs. I divided the forest operations process into four phases (felling, extraction, processing, and loading) to analyze the machine’s cost and productivity. In the thinning studies, there were various forest machines and tools used for forest thinning operations, and the productivity of each machine was determined by different variables. Here I summarized the common factors driving thinning productivity and costs. For example, tree diameter and machine travel distance commonly affected thinning productivity. The average cost of forest thinning was lowest for a mechanized whole-tree thinning operation at $20.27/metric ton or $2,779/ha. Feller-bunchers and skidders showed the highest productivity in felling and extraction machines, respectively. I found that extraction cost in the process of stump-to-truck forest harvesting accounted for the largest proportion of the cost of forest thinning. With the cost data from the selected studies, I developed a spreadsheet-based model for estimating thinning costs associated with various harvesting systems. The model calculates the productivity and cost of the machine used in the stump-to-truck thinning process based on user input information. The results of this literature synthesis and our new thinning cost model and tool can help foresters develop a cost-effective plan for thinning operations, which can drive down the cost of thinning and help meet forest management objectives more efficiently